Re: [PATCH net-next v8 2/6] net: pcs: xpcs: re-initiate clause 37 Auto-negotiation

[Choong Yong Liang]

On 26/2/2025 11:40 pm, Russell King (Oracle) wrote:
> On Wed, Feb 26, 2025 at 03:48:33PM +0800, Choong Yong Liang wrote:
> > diff --git a/drivers/net/pcs/pcs-xpcs-wx.c b/drivers/net/pcs/pcs-xpcs-wx.c
> > index fc52f7aa5f59..f73ab04d09f0 100644
> > --- a/drivers/net/pcs/pcs-xpcs-wx.c
> > +++ b/drivers/net/pcs/pcs-xpcs-wx.c
> > @@ -172,11 +172,9 @@ int txgbe_xpcs_switch_mode(struct dw_xpcs *xpcs, phy_interface_t interface)
> >   		return 0;
> >   	}
> >   
> > -	if (xpcs->interface == interface && !txgbe_xpcs_mode_quirk(xpcs))
> > +	if (!txgbe_xpcs_mode_quirk(xpcs))
> >   		return 0;
> >   
> > -	xpcs->interface = interface;
> > -
>
> ...
>
> > --- a/drivers/net/pcs/pcs-xpcs.c
> > +++ b/drivers/net/pcs/pcs-xpcs.c
> > @@ -602,12 +602,37 @@ static void xpcs_get_interfaces(struct dw_xpcs *xpcs, unsigned long *interfaces)
> >   		__set_bit(compat->interface, interfaces);
> >   }
> >   
> > +static int xpcs_switch_interface_mode(struct dw_xpcs *xpcs,
> > +				      phy_interface_t interface)
> > +{
> > +	int ret = 0;
> > +
> > +	if (xpcs->interface != interface) {
> > +		if (xpcs->info.pma == WX_TXGBE_XPCS_PMA_10G_ID) {
> > +			ret = txgbe_xpcs_switch_mode(xpcs, interface);
> > +			if (ret)
> > +				return ret;
>
> The above modification changes the functionality.
>
> In the old code, txgbe_xpcs_switch_mode() does its work when
> xpcs->interface is not the same as interface OR txgbe_xpcs_mode_quirk()
> is true.
>
> Your replacement code calls txgbe_xpcs_switch_mode() when
> xpcs->interface is not the same as interface, *and* it can do its
> work when txgbe_xpcs_mode_quirk() returns true.
>
> So, e.g. when txgbe_xpcs_mode_quirk() returns false, but the interface
> changes, txgbe_xpcs_mode_quirk() used to do its work, but as a result
> if your changes, it becomes a no-op.
>
> The point of txgbe_xpcs_mode_quirk() is to always do the work if it
> returns true, even if the interface mode doesn't change.
>
> Therefore, this patch is logically incorrect, and likely breaks TXGBE.
Thank you for pointing out the oversight. I will review the logic and make 
the necessary corrections to ensure the patch does not disrupt the expected 
behavior.